Hitchcock Murder Mystery Script: The witness at the marina said that Scott Peterson was smiling while retrieving his boat from the slip. It sounds like he was congratulating himself for what he thought was pulling off the perfect crime.
Then, believing the bodies would never surface, (by his own doing) he entangles himself as a victim in the case by producing the marina parking slip to document his alibi and thusly documents placing himself at the scene of where the bodies are discovered.
The irony of how he entrapped himself will stand out long after he is executed.
Now that's what I like to call "poetic justice"! The two bodies he murdered were the two bodies that came back to be his worst nightmare and ultimately got him arrested. What comes around goes around!!!